Electronics Cookbook

Chapter 14. LEDs and Displays

14.0 Introduction

LEDs can be used both for illumination and as indicators. They can also be arranged as 7-segment displays or as tiny pixels in an OLED (organic LED) display.

This chapter contains recipes relating to powering and controlling LEDs as well as for using a display with an Arduino or Raspberry Pi.

14.1 Connect Standard LEDs

Problem

You want to connect a standard low-power LED to a GPIO pin, but you are not sure what value of series resistor to use.

Solution

Back in Recipe 4.4 you saw how an LED needs a series resistor to prevent too much current from flowing. Too much current will shorten the life of an LED, but more importantly, it may damage or destroy the Arduino or Raspberry Pi GPIO pin that is controlling the LED.

Wire up your LED to a GPIO pin as shown in Figure 14-1 and then use Table 14-1 to select a value for the series resistor.

Figure 14-1. Connecting an LED to a GPIO Pin

Table 14-1. LED Series Resistor Values

	Infrared	Red	Orange/Yellow/Green	Blue/White	Violet	UV
Vf	1.2-1.6V	1.6-2V	2-2.2V	2.5-3.7V	2.7-4V	3.1-4.4V
3.3V GPIO 3mA	1kΩ	680Ω	470Ω	270Ω	220Ω	68Ω
3.3V GPIO 16mA	150Ω	120Ω	82Ω	56Ω	39Ω	15Ω
5V GPIO 20mA	220Ω	180Ω	150Ω	150Ω	120Ω	100Ω

Discussion

In practice, nearly all LEDs will illuminate to some degree even from 3.3V with a 1kΩ resistor limiting the current. So, as an even broader rule of thumb, ...